In general, such sequencing apparatus consists of a separation media, typically polyacrylamide gel, constrained between glass plates. Prepared DNA samples are introduced into one end of the gel. Each end of the gel is coupled to a high voltage electrode by means of an electrolyte buffer solution. A high voltage electric field is applied to the gel, causing the DNA molecules to migrate in relation to their size. The DNA is not readily detectable alone, and the samples are typically labeled with radioactive or fluorescent dyes, enabling secondary detection through autoradiographic film or optical sensing.
Conventional sequencing gels are operated with the gels placed vertically. This does not facilitate good heat transfer in the gel medium, and limitations are imposed to the amount of power that can be dissipated from the gel or by the cell. This power limitation also limits the strength of the electric field that can be applied to the gel, and hence it limits the speed with which the separation can be performed. Conventional separations take 2 to 8 hours and typically have a gel thickness of 0.2 to 3 mm. This makes possible a thermal gradient upon the gel, which gradient can limit the resolution of the migrating molecules since this migration is temperature dependent.
A U.S. Patent application filed Dec. 20, 1990 and titled "Horizontal Gel Electrophoresis Apparatus," is licensed to the assignee hereof and is incorporated herein by reference. This application discloses a device, hereinafter referred to as the "Brumley/Smith Apparatus," which improves upon prior art by its horizontal water cooled layout and ultrathin slab gel (approximately 60 microns typical). These features facilitate improved speed and resolution by allowing efficient heat transfer and minimizing thermal gradients across the gel material. Much higher electric fields across the gel are possible, resulting in reduced time to separate. A typical duration is 15-20 minutes.